Background Art
Butanol is an important industrial chemical with a variety of applications, including use as a fuel additive, as a feedstock chemical in the plastics industry, and as a food-grade extractant in the food and flavor industry. Accordingly, there is a high demand for butanol, as well as for efficient and environmentally friendly production methods.
Production of butanol utilizing fermentation by microorganisms is one such environmentally friendly production method. Some microorganisms that produce butanol in high yields also have low butanol toxicity thresholds, such that butanol needs to be removed from the fermentor as it is being produced. In situ product removal (ISPR) may be used to remove butanol from the fermentor as it is produced, thereby allowing the microorganism to produce butanol at high yields. One method for ISPR that has been described in the art is liquid-liquid extraction (U.S. Patent Application Publication No. 2009/0305370). In order to be technically and economically viable, liquid-liquid extraction requires contact between the extractant and the fermentation broth for efficient mass transfer; phase separation of the extractant from the fermentation broth (during and after fermentation); and/or efficient recovery and recycle of the solvent and minimal degradation and/or contamination of the extractant over a long-term operation.
When the aqueous stream entering the fermentor contains undissolved solids from the feedstock, the undissolved solids interfere with the requirements noted above for liquid-liquid extraction to be technically and economically viable by increasing capital and operating costs. In particular, the presence of the undissolved solids during extractive fermentation may lower the mass transfer coefficient inside the fermentor, impede phase separation in the fermentor, may result in the accumulation of oil (e.g., corn oil) from the undissolved solids in the extractant leading to reduced extraction efficiency over time, may increase the loss of solvent because it becomes trapped in solids ultimately removed as Dried Distillers' Grains with Solubles (DDGS), may slow the disengagement of extractant drops from the fermentation broth, and/or may result in a lower fermentor volume efficiency. Thus, there is a continuing need to develop more efficient methods and systems for producing product alcohols such as butanol through extractive fermentation.
The present invention satisfies the above need and provides methods and systems for producing product alcohols such as butanol by decreasing the amount of undissolved solids that are fed to the fermentor.